In the past, a technique has been introduced for providing a scroll compressor in which a suction capacity regulating mechanism is installed in an end plate of a fixed scroll (see Japanese Laid-open Patent Application No. 2007-154761, for example).
This suction capacity regulating mechanism is primarily composed of a through hole which penetrates through the end plate of the fixed scroll and opens at the bottom of a spiral groove of the fixed scroll, a fluid introducing passage which connects to the through hole, a piston which is inserted into the through hole, a biasing member which biases the piston toward a side of the fluid introducing passage in the through hole, and a metal piston ring which is fitted into an annular groove of the piston and which has a right-angled fitting end. The suction capacity regulating mechanism regulates a suction capacity of a scroll compressing mechanism by switching between a regulating operation condition involving a connection between “a first compression chamber formed between an inner circumferential surface of a wrap of the fixed scroll and an outer circumferential surface of a wrap of a movable scroll” and “a second compression chamber formed between an outer circumferential surface of the wrap of the fixed scroll and an inner circumferential surface of the wrap of the movable scroll” and a normal operation condition of shut-off between the first compression chamber and the second compression chamber (a condition that utilizes 100% of the suction capacity). Specifically, when a fluid that applies a pressure larger than biasing force of the biasing member per unit area is introduced into the fluid introducing passage, the piston is pushed down and a space at a lower end of the through hole is shut. The suction capacity regulating mechanism is turned to a condition of shut-off between the first compression chamber and the second compression chamber, that is, a normal operation condition. On the other hand, when a fluid that applies a pressure lower than biasing force of the biasing member per unit area is introduced into the fluid introducing passage, the piston is pushed up and the space at the lower end of the through hole is open. The suction capacity regulating mechanism is turned to a condition involving a connection between the first compression chamber and the second compression chamber, that is, a regulating operation condition.